From the onset of the campaign, both parties considered Johnson one of the GOP's most vulnerable members. The freshman senator, who unseated Feingold six years ago, trailed the Democrat in nearly every poll of the race this year, sometimes by more than 10 points in the race's early going.

But a plethora of Democratic and Republican groups made late, unexpected investments in the race’s final weeks, signaling that it had become surprisingly close.

Coming into Election Day, the race was rated Tilts Democrat by the Rothenberg & Gonzales Political Report/Roll Call.

After nearly six years in the Senate, two as chairman of the Homeland Security and Governmental Affairs Committee, Johnson ran for re-election as an outsider against Feingold.

A novice who’d never run for office before, Johnson defeated Feingold in 2010 with nearly 52 percent of the vote. His victory marked the first time in nearly a quarter century that a Republican had won a Senate election in Wisconsin.

Johnson got a hand from Speaker Paul D. Ryan, who stumped for the Republican candidate during the last four days of the campaign.